Probabilistic Bullheading Analysis is a Unique Risk Assessment Tool for Drilling and Completion Equipment Selection for Critical HP/HT Wells

摘要

This paper discusses the development and validation of the application of probabilistic bullheading analysis. Bullheading is the process of pumping fluid from the surface to the bottom of the wellbore in an attempt to deliver suitably weighted fluid to force fluid or gas from a given formation back into the formation. The methodology and procedure described in this paper provide a quantitative basis for risk analysis and equipment selection for high-profile wells, with focus on high-pressure/high-temperature (HP/HT) subsea well developments. As a result of this methodology, an accurate and risk-based approach can be taken using a probabilistic distribution of risks and pressure involved during bullheading operations. The probabilistic model for performing bullheading analysis is based on the Monte Carlo method using statistical distribution of the parameters, which include reservoir properties, reservoir fluid properties, wellbore structure, and bullheading fluid properties. Each bullheading simulation assumes the wellbore is filled with the formation fluid and determines the shut-in pressure. Then, bullheading simulation considers the changes in pressure-volume-temperature (PVT) properties, fluid loss into the formation, fracture initiation, and compressibility of the fluids. Each probabilistic simulation run performs 2,000 simulations. The shut-in pressure and maximum pumping pressures are recorded to provide probabilistic distributions for risk-based analysis. The application of the methodology is demonstrated using an example case study. A special emphasis is placed on performing a quality check of the statistical data to mitigate any skewedness that might occur during the simulations. A total of 24,000 simulations were performed to provide the distribution of pressure during the bullheading operation. The results can be presented in a variety of plots, including maximum bullheading pressures, maximum shut-in pressures, probability of fracturing, and the effect of pressure depletion.